1. Field of the Invention
The present invention relates to an optical reading and writing device for use in CD players, video disk players, and so on.
2. Description of the Prior Art
When information is written on or read from an optical disk such as a video disk by means of an optical reading and writing device, the quality of writing or reading signals is degraded when the optical disk is warped or bent cambered at its outer circumference. The conventional methods to compensate the signal degradation due to the tilt of the optical disk are to detect the tilt of the optical disk by means of a tilt sensor and then tilt the whole optical reading and writing device using the detected tilt signal.
One example of an optical reading and writing device having a tilt sensor is described in U.S. Pat. No. 5,218,597. In such a conventional scheme, however, since a sensor is mounted on a main body frame of the optical reading and writing device, a measured value is a relative tilt of an optical disk with respect to the main body frame. Therefore, compensation of the tilt of the optical disk is made by tilting the whole optical reading and writing device. Optical reading and writing devices having this kind of scheme, therefore, must have a heavy mechanism to tilt itself and must be necessarily large.
Another example for a conventional optical reading and writing device is explained below. In this example the drawback of the first example was resolved by tilting only an objective lens to compensate signal degradation due to a tilt of an optical disk. One example of this type of optical reading and writing device is described in Japanese Utility Model Laid Open Publication No. 60-135817. In this scheme a relative tilt of an optical disk with respect to an objective lens must be detected. A method to measure the relative tilt is, as described in Japanese Utility Model Laid Open Publication No. 60-135817, to mount a light source and photo detectors on a movable objective lens holder.
In this conventional scheme, however, the movable objective lens holder carries additional masses of the light source and photodetectors. Further, wirings to supply an electric power to the light source and to receive output signals from the photodetecors degrades the drivability of the objective lens.